1. Field of the Invention
The present invention relates to a photosensitive polymer.
2. Description of the Related Art
As semiconductor devices become highly integrated, photolithography processes used in the manufacture of such devices must be capable of fine pattern formation. Further, as a result of sub-quarter micron or smaller sized patterns which are needed in semiconductor memory devices having capacities exceeding 1 Gbit, a photolithography technique has been proposed in which an argon fluoride (ArF) excimer laser (wavelength: 193 nm) is used as a new type of exposure light source. The use of the ArF excimer laser stems from the fact that its wavelength is less than that of the more conventional krypton fluoride (KrF) excimer laser (wavelength: 248 nm). As a result, there is an increasing demand for new chemically amplified photoresist polymers and photoresist compositions which are suitable for use with the ArF excimer laser.
In general, a chemically amplified photoresist composition for an ArF excimer laser should preferably exhibit the following characteristics: (1) transparency at a wavelength of 193 nm; (2) excellent thermal properties (for example, high glass transition temperature); (3) good adhesion to underlying and overlying film materials; (4) high resistance to dry etching; and (5) easily capable of being developed using developing solutions which are in widespread use in the manufacture of semiconductor devices, for example, 2.38% by weight of tetramethyl ammonium hydroxide (TMAH).
However, a terpolymer comprising methylmethacrylate, t-butyl methacrylate and methacrylic acid, which is a widely known chemically amplified photoresist polymer for the ArF excimer laser, does not exhibit all of the above-described characteristics. In particular, the terpolymer has a very low resistance to dry etching and a low adhesion to underlying and overlying film materials.
Recently, attempts have been made to prepare photosensitive polymers for the ArF excimer laser having increased etching resistances using (meth)acrylate which has alicyclic compounds, for example, isobornyl, adamantyl or tricyclodecanyl group, as a substitutent or t-butyl norbornene carboxylate. However, these polymers also have several disadvantages. For example, their etching resistance and adhesion characteristics to film materials are still poor, which results in lifting of photoresist patterns.
It is an objective of the present invention to provide a photosensitive polymer which maintains transparency even when exposed to a short-wavelength light source of 193 nm or below, and which has improved adhesive, contrast, and resistance to dry etching characteristics.
It is another objective of the present invention to provide a chemically amplified photoresist composition containing the photosensitive polymer.
Accordingly, to achieve the above objective, there is provided a photosensitive polymer including a first monomer which is an alicyclic hydrocarbon carboxylate having an acid-labile C8 to C20 tertiary alicyclic hydrocarbon group as a substituent, and a second monomer which is capable of free radical polymerization.
Preferably, the alicyclic hydrocarbon carboxylate is norbornene carboxylate, the second monomer is maleic anhydride, and the C8 to C20 tertiary alicyclic hydrocarbon group is 2-methyl-2-norbornyl, 2-methyl-2-isobornyl, 8-ethyl-8-tricyclo[5.2.1.02,6]decanyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl or 1-adamantyl-1-methyl ethyl.
The photosensitive polymer according to present invention is polymerized with one or more monomers selected from the group consisting of a third monomer, a fourth monomer and a fifth monomer, in addition to the first and second monomers, wherein the third monomer is a monomer having a secondary cyclic alcohol group bonded to its backbone; wherein the fourth monomer is a monomer selected from the group consisting of (meth)acrylic acid, (meth)acrylate having C1 to C12 aliphatic alcohol as a substituent, (meth)acrylate having an acid-labile group as a substituent, and (meth)acrylate having a dissolution inhibitor group as a substituent; and wherein the fifth monomer is a monomer selected from the group consisting of norbornene, norbornene-ol, norbornene having C1 to C12 aliphatic alcohol as a substituent, norbornene carboxylic acid, norbornene dicarboxylic anhydride, norbornene carboxylate having C1 to C12 aliphatic alcohol as a substituent, norbornene carboxylate having a lactone group as a substituent, norbornene carboxylate having an acid-labile group as a substituent, and norbornene carboxylate having a dissolution inhibitor group as a substituent.
Preferably, the third monomer is secondary polycyclic alcohol.
The photosensitive polymer according to the preferred embodiment of the present invention has a cyclic backbone, and an acid-labile C8 to C20 tertiary alicyclic hydrocarbon group is bonded to the backbone. Thus, a photoresist composition containing the same exhibits a high resistance to etching. Also, since there is a large difference in the solubility before and after exposure, the contrast is excellent.
A photosensitive polymer and a chemically amplified photoresist composition containing the same according to the present invention will now be described. Also, a preferred photolithography process using the chemically amplified photoresist composition will be described. This invention may, however, be embodied in many different forms, and these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
A photosensitive polymer according to the present invention includes a first monomer which is an alicyclic hydrocarbon carboxylate having an acid-labile C8-C20 tertiary alicyclic hydrocarbon group as a substituent and a second monomer capable of free radical polymerization. The weight average molecular weight of the photosensitive polymer is preferably in the range of 1,000 to 100,000.
Suitable alicyclic hydrocarbons constituting a backbone of the first monomer include norbornene, isobornene, adamantene and the like.
2-methyl-2-norbornyl, 2-methyl-2-isobornyl, 8-ethyl-8-tricyclo[5.2.1.02,6]decanyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl or 1-adamantyl-1-methylethyl is preferably used as the C8-C20 tertiary alicyclic hydrocarbon group, which can be expressed by the formula below. Since the alicyclic hydrocarbon group is a tertiary alkyl group, it is acidolyzed. 
Suitable second monomers capable of free radical polymerization to introduce a first monomer into the photosensitive polymer include maleic anhydride.
The photosensitive polymer according to the present invention has a cyclic backbone like in an alicyclic hydrocarbon or maleic anhydride. Also, since a C6-C20 tertiary alicyclic hydrocarbon group is bonded to the backbone of the polymer, the etching resistance of the photosensitive polymer is much larger than that of the conventional photosensitive polymer.
The etching resistance of a polymer is generally known to be inversely proportion to an Ohnishi parameter, which is calculated by the following formula (1):
Ohnishi parameter=NT/Ncxe2x88x92No
wherein NT is the total number of atoms in the polymer, Nc is the number of carbon atoms in the polymer and No is the number of oxygen atoms in the polymer.
Table 1 lists Ohnishi parameters calculated by the formula (1) in the prior art polymer and in the polymer of the present invention.
It is generally known that dry etching resistance is good when the Ohnishi parameter is less than or equal to 3.4, preferably less than or equal to 3.2. From Table 1, it is predictable that the dry etching resistance of the polymer according to the present invention is substantially improved when compared to that of the conventional polymer.
It is preferred that the photosensitive polymer according to the present invention further includes another monomer capable of enhancing characteristics required for the photosensitive polymer.
That is, it is advantageous that the photosensitive polymer according to the present invention is a terpolymer having a third monomer combined with the first and second monomers.
The third monomer is preferably a molecule having a secondary cyclic alcohol group. The third monomer having a secondary cyclic alcohol group increases the etching resistance of the polymer and noticeably increases the adhesion to underlying film materials. In particular, a secondary alcohol group, which is chemically stable, is advantageous, since it can be maintained for a long time.
As the third monomer, secondary polycyclic alcohol is more preferably used. For example, secondary C10 to C15 tricyclo alcohol is suitably used as the third monomer.
Another terpolymer according to the present invention is a terpolymer having a fourth monomer combined with the first and second monomers.
The fourth monomer is preferably a monomer selected from the group consisting of (meth)acrylic acid, (meth)acrylate having C1 to C12 aliphatic alcohol as a substituent, (meth)acrylate having an acid-labile group as a substituent, and (meth)acrylate having a dissolution inhibitor group as a substituent.
The fourth monomer is selected according to the properties necessary for use in a photosensitive polymer.
In order to enhance the adhesion of the polymer, (meth)acrylic acid or (meth)acrylate having C1 to C12 aliphatic alcohol as a substituent is used.
In the case where it is a critical issue to enhance contrast, (meth)acrylate having an acid-labile group as a substituent is used. The acid-labile group refers to a group which allows the polymer to exhibit non-dissolution in a developing solution when it is bonded to the polymer but to exhibit dissolution when it is acidolyzed.
In the case where a large number of hydrophilic functional groups are present in another monomer constituting the polymer, so that an unexposed region may also be developed with a conventional developing solution, (meth)acrylate having a dissolution inhibitor group as a substituent is preferably used as the monomer. The dissolution inhibitor group refers to a group which is a hydrophobic group that is not acidolyzed by an acid generated by exposure.
When it is necessary to enhance the wettability against the developing solution, (meth)acrylate is preferably used.
Preferably, the C1 to C12 aliphatic alcohol pendent to (meth)acrylate is 2-hydroxyethyl, the acid-labile group pendent to (meth)acrylate is t-butyl or C6 to C20 tertiary alicyclic hydrocarbon, and the dissolution inhibitor group pendent to (meth)acrylate is methyl or C7 to C20 aliphatic hydrocarbon. Examples of the C7 to C20 tertiary alicyclic hydrocarbon include adamantyl, norbornyl or isobornyl.
Still another terpolymer according to the present invention is a terpolymer having a fifth monomer combined with the first and second monomers.
The fifth monomer is preferably a monomer selected from the group consisting of norbornene, norbornene-ol, norbornene having C1 to C12 aliphatic alcohol as a substituent, norbornene carboxylic acid, norbornene dicarboxylic anhydride, norbornene carboxylate having C1 to C12 aliphatic alcohol as a substituent, norbornene carboxylate having a lactone group as a substituent, norbornene carboxylate having an acid-labile group as a substituent, and norbornene carboxylate having a dissolution inhibitor group as a substituent.
In terms of the kind of monomers selected, the fifth monomer is also selected according to the properties necessary for use in a photosensitive polymer.
In the case where it is necessary to enhance adhesion of a polymer or to reduce swelling of a photoresist pattern having the polymer as a main component, norbornene-ol, norbornene having C1 to C12 aliphatic alcohol as a substituent, norbornene carboxylate having C1 to C12 aliphatic alcohol as a substituent, norbornene dicarboxylic anhydride or norbornene carboxylate having a lactone group as a substituent, is preferably used.
In particular, in the case where norbornene dicarboxylic anhydride or norbornene carboxylate having a lactone group as a substituent is used as the monomer, the adhesion is improved, and a photoresist pattern formed using the same has an excellent profile without roughness.
In the case where it is a critical issue to enhance contrast, norbornene carboxylate having an acid-labile group as a substituent is used.
In the case where a large number of hydrophilic functional groups are present in another monomer constituting the polymer so that an unexposed region may also be developed with a conventional developing solution, norbornene carboxylate having a dissolution inhibitor group as a substituent is preferably used as the monomer.
When it is necessary to enhance the wettability against the developing solution, norbornene carboxylic acid-is preferably used.
Preferably, the C1 to C12 aliphatic alcohol pendent to norbornene is 2-hydroxymethyl, the C1 to C12 aliphatic alcohol pendent to norbornene carboxylate is 2-hydroxyethyl, the lactone group pendent to norbornene carboxylate is 2,4 dihydroxy-3,3-dimethyl butyric acid lactone or 2(3),4 dihydroxy butyric acid lactone, the acid-labile group pendent to norbornene carboxylate is t-butyl, tetrahydropyranyl or 1-alkoxyethyl, and the dissolution inhibitor group pendent to norbornene carboxylate is methyl.
As occasion demands, the photosensitive polymer according to the present invention may be a tetrapolymer having a fourth or fifth polymer polymerized with the first, second and third monomers. As described above, the monomer ratio can be adjusted according to properties required for use in the photosensitive polymer. A tetrapolymer having the first, second, fourth and fifth monomers polymerized therein can also be used as the photosensitive polymer according to the present invention.
The photosensitive polymer according to the present invention can be represented by the formula (1): 
wherein R1 is an acid-labile C8 to C20 tertiary alicyclic hydrocarbon group;
R2 is hydrogen or methyl;
R3 is hydrogen, C1 to C12 aliphatic alcohol, an acid-labile group or a dissolution inhibitor group;
R4 is hydrogen, hydroxy, C1 to C12 aliphatic alcohol, carboxy, oxycarbonyl having C1 to C12 aliphatic alcohol pendant group, oxycarbonyl having a lactone pendant group, oxycarbonyl having an acid-labile pendant group, oxycarbonyl having a dissolution inhibitor pendant group or carboxylic anhydride linked to R5;
R5 is hydrogen, hydroxy, C1 to C12 aliphatic alcohol, carboxy, oxycarbonyl having C1 to C12 aliphatic alcohol pendant group, oxycarbonyl having a lactone pendant group, oxycarbonyl having an acid-labile pendant group, oxycarbonyl having a dissolution inhibitor pendant group or carboxylic anhydride linked to R4;
x is an integer in the range of 1 to 5;
l, m, n, p and q are integers; and
l/(l+m+n+p+q) equals 0.0 to 0.3, m/(l+m+n+p+q) equals 0.0 to 0.3, n/(l+m+n+p+q) equals 0.1 to 0.6, p/(l+m+n+p+q) equals 0.1 to 0.6, and q/(l+m+n+p+q) equals 0.0 to 0.5.
The weight average molecular weight of the polymer is preferably in the range of 1,000 to 100,000.
Most preferably, examples of R1 include 2-methyl-2-norbornyl, 2-methyl-2-isobornyl, 8-ethyl-8-tricyclo[5.2.1.02,6]decanyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl or 1-adamantyl-1-methylethyl. In R3, the C1 to C12 aliphatic alcohol is 2-hydroxyethyl, the acid-labile group is t-butyl or C8 to C20 tertiary alicyclic hydrocarbon, and the dissolution inhibitor group is methyl or C7 to C20 aliphatic hydrocarbon. Examples of the C7 to C20 aliphatic hydrocarbon include isobornyl, norbornyl or adamantyl.
In either R4 or R5, it is preferred that the C1 to C12 aliphatic alcohol is hydroxymethyl, the oxycarbonyl having C1 to C12 aliphatic alcohol pendant group is 2-hydroxyethyloxycarbonyl, oxycarbonyl having a lactone pendant group is 2,4 dihydroxy-3,3-dimethyl butyric acid lactonyl oxycarbonyl or 2(3),4 dihydroxy butyric acid lactonyl oxycarbonyl, oxycarbonyl having an acid-labile pendant group is t-butyloxycarbonyl, tetrahydropyranyloxycarbonyl or 1-alkoxyethyloxycarbonyl, and the oxycarbonyl having a dissolution pendant inhibitor group is methyloxycarbonyl.
Since the backbone of the photosensitive polymer according to the present invention has a cyclic structure, the etching resistance thereof is large. In particular, since the C8 to C20 tertiary hydrocarbon group is bonded to the backbone, the etching resistance is further increased. Also, when a secondary cyclic alcohol group is bonded to the backbone, the polymer also exhibits good adhesion to underlying layers and high wettability to a developing solution, and the etching resistance is further increased.
A chemically amplified photoresist composition of the present invention includes the above-described photosensitive polymer and a photoacid generator. The photoacid generator is preferably contained in an amount of 1 to 15% by weight based on the total weight of the photosensitive polymer. The photoacid generator is preferably a substance that has a high thermal stability. Therefore, suitable photoacid generators include triarylsulfonium salts, diaryliodonium salts, sulfonates or N-hydroxysuccinimide triflates.
Examples of photoacid generators include triphenylsulfonium triflate, triphenylsulfonium antimonate, diphenyliodonium triflate, diphenyliodonium antimonate, methoxydiphenyliodonium triflate, di-t-butyldiphenyliodonium triflate, 2,6-dinitro benzyl sulfonate, pyrogallol tris(alkyl-sulfonates), pyrogalloltris(alkylsulfonates)), norbornene-dicarboximide triflate, triphenylsulfonium nonaflate, diphenyliodonium nonaflate, methoxydiphenyliodonium nonaflate, di-t-butyldiphenyliodonium nonaflate, N-hydroxysuccinimide nonaflates, norbornene dicarboximide nonaflate, triphenylsulfonium perfluorooctanesulfonates, diphenyliodonium perfluorooctanesulfonates, methoxydiphenyliodonium perfluorooctane sulfonates, di-t-butyldiphenyliodonium triflate, N-hydroxysuccinimide perfluorooctanesulfonates, or norbornene dicarboximide perfluorooctanesulfonates.
Preferably, the photoresist composition of the present invention further includes 0.01 to 10% by weight of organic base based on the total weight of the photosensitive polymer. Suitable organic bases include triethylamine, triisobutylamine, triisooctylamine, diethanolamine, triethanolamine or a mixture thereof. The organic base is added for preventing a pattern deformation, which results from an unexpected acidolysis caused by the acid generated at the exposed regions and then diffused into the unexposed regions.
Also, the chemically amplified photoresist composition according to the present invention includes 30 to 200 ppm of an organic or base surfactant, which functions to allow the photoresist composition to be uniformly coated on a substrate.
Cyclopentadiene is dissolved in an organic solvent and then acrylate having a C8 to C20 tertiary alicyclic hydrocarbon group as a substituent is added thereto to prepare a first monomer (I) as expressed by the following reaction scheme (1): 
wherein R1 is a C8 to C20 tertiary alicyclic hydrocarbon group.
Preferably, R1 is 2-methyl-2-norbornyl, 2-methyl-2-isobornyl, 8-ethyl-8-tricyclo[5.2.1.02,6]decanyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl or 1-adamantyl-1-methylethyl.
The monomer (I) prepared in the above-described manner, a second monomer (II), a third monomer (III), a fourth monomer (IV) and a fifth monomer (V) are dissolved in an organic solvent, for example, toluene, in a mixture ratio of p:n:m:q:l, and then a polymerization initiator, e.g., azobisisobutyronitrile (AIBN) is added thereto to carry out polymerization to prepare a polymer, as expressed by the following reaction scheme (2), and the polymerization ratio is the same as defined in the above formula (1): 
The chemically amplified photoresist composition according to the present invention is prepared by dissolving the photosensitive polymer prepared in the above-described manner and a photoacid generator, in an appropriate solvent, and mixing the same. Here, the photoacid generator is mixed in an amount of 1 to 15% by weight based on the weight of the polymer. Also, it is preferable to complete the photoresist composition by further dissolving 0.01 to 10% by weight of an organic base based on the weight of the polymer. Also, 30 to 200 ppm of a surfactant is preferably further included in the composition.
The chemically amplified photoresist composition prepared in the above-described manner can be used for a general photolithography process, and is particularly suitable for forming a fine pattern to satisfy a design rule of 0.25 xcexcm or smaller using an ArF excimer laser as an exposure light source.
First, the photoresist composition is coated on a substrate where a patterning object material is formed, to form a photoresist layer having a predetermined thickness, preferably 0.2 to 2 xcexcm. Subsequently, pre-baking is carried out on the photoresist layer. The pre-baking step is performed at a temperature of 70 to 160xc2x0 C. for 30 to 360 seconds. After the pre-baking step, the photoresist layer is exposed using a mask having a predetermined pattern, using an exposure light source having a wavelength of 248 nm or less, preferably an ArF excimer laser having a wavelength of 193 nm. Acid is generated in the photoacid generator contained in the photoresist layer by exposure. The photosensitive polymer is acidolyzed by the catalytic action of the thus-generated acid, as expressed by reaction scheme 3. As a result, a large amount of hydrophilic groups, e.g., carboxy groups, are produced in the exposed portion of the photoresist layer. Thus, a noticeable difference in the polarity of the photoresist layer is created between an exposed region and an unexposed region. That is to say, contrast is noticeably increased. 
The parenthesis enclosing R3 represent that R3 is not acidolyzed but is retained since it is a dissolution inhibitor group or C1 to C12 aliphatic alcohol. The parenthesis enclosing xe2x80x94COOH next to R4 represent a carboxy group remaining after R4 is acidolyzed in the case where R4 is a carboxyl group or an oxycarbonyl group having a acid-labile group as a substituent.
After exposure, the photoresist layer is thermally treated for a short time before development, which is referred to as a post-exposure-thermal treatment. The post-exposure-thermal treatment is performed for the purpose of increasing contrast by further activating acidolysis of exposed regions by the acidic catalyst, to acidolyze ester or acidic anhydride contained in the photosensitive polymer into carboxy groups.
Next, development is performed using an appropriate developing solution to complete a photoresist pattern. Here, the developing solution used is a developing solution for general development processes, for example, 2.38% by weight of tetramethylammonium hydroxide (TMAH). In the case where a dissolution inhibitor group is bonded to the backbone of the photosensitive polymer constituting the photoresist layer, since the photoresist layer in the unexposed region is not easily dissolved in the developing solution, the thickness of the photoresist layer in the unexposed region is not reduced, unlike the conventional art.
After forming the photoresist pattern, a patterning object layer is etched to form a desired pattern. The photoresist pattern of the present invention is formed of a photoresist layer including a photosensitive polymer having a cyclic backbone and a C8 to C20 tertiary alicyclic hydrocarbon pendent to the backbone, and thus the etching resistance thereof is large. Therefore, a pattern having a good profile, that is, having a precise critical dimension, can be formed.